This project studies the organization of social and cognitive behaviors in 3-year-old-children. Samples consist of 65 males and 66 females ranging in age from two and a half to three years of age. Data from a research nursery school are based on observations in three different free play settings as well as performance in a number of experimental tests of coping with barrier situations. Reliable subjective ratings are included to cover the areas of social, emotional and attentional behavior. Cognitive and language behaviors in the young children are assesed by a variety of standardized tests. Analyses cover sex-differences, activity level, and cross-setting and cross-time stabilities of behavior.